(a) An owner or operator may achieve compliance with the nitrogen oxides (NOX ) emission specifications of §117.105 of this title (relating to Emission Specifications for Reasonably Available Control Technology (RACT)) or §117.110 of this title (relating to Emission Specifications for Attainment Demonstration) by achieving equivalent NOX emission reductions obtained by compliance with a plant-wide emission specification. Any owner or operator who elects to comply with a plant-wide emission specification shall reduce emissions of NOX from affected units so that if all such units were operated at their maximum rated capacity, the plant-wide emission rate of NOX from these units would not exceed the plant-wide emission specification as defined in §117.10 of this title (relating to Definitions).
(b) The owner or operator shall establish an enforceable NOX emission limit for each affected unit at the source as follows.
  (1) For boilers and process heaters that operate with a continuous emissions monitoring system (CEMS) or predictive emissions monitoring system (PEMS) in accordance with §117.140 of this title (relating to Continuous Demonstration of Compliance), the emission specifications apply in:
    (A) the units of the applicable standard (the mass of NOX emitted per unit of energy input (pounds per million British thermal units (lb/MMBtu) or parts per million by volume (ppmv)), on a rolling 30-day average period; or
    (B) as the mass of NOX emitted per hour (pounds per hour), on a block one-hour average.
  (2) For boilers and process heaters that do not operate with CEMS or PEMS, the emission specifications apply as the mass of NO X emitted per hour (pounds per hour), on a block one-hour average.
  (3) For stationary gas turbines, the emission specifications apply as the NOX concentration in ppmv at 15% oxygen (O2), dry basis on a block one-hour average.
  (4) For stationary internal combustion engines, the NOX emission specifications apply in units of grams per horsepower-hour (g/hp-hr) on a block one-hour average.
(c) An owner or operator of any gaseous and liquid fuel-fired unit that derives more than 50% of its annual heat input from gaseous fuel shall use only the appropriate gaseous fuel emission specification of §117.105 or §117.110 of this title at maximum rated capacity in calculating the plant-wide emission specification and shall assign to the unit the maximum allowable NOX emission rate while firing gas, calculated in accordance with subsection (a) of this section. The owner or operator shall also:
  (1) comply with the assigned maximum allowable emission rate while firing gas only;
  (2) comply with the liquid fuel emission specification of §117.105 of this title while firing liquid fuel only; and
  (3) comply with a limit calculated as the actual heat input weighted sum of the assigned gas-firing allowable emission rate and the liquid fuel emission specification of §117.105 of this title while operating on liquid and gaseous fuel concurrently.
(d) An owner or operator of any gaseous and liquid fuel-fired unit that derives more than 50% of its annual heat input from liquid fuel shall use a heat input weighted sum of the appropriate gaseous and liquid fuel emission specifications of §117.105 or §117.110 of this title in calculating the plant-wide emission specification and shall assign to the unit the maximum allowable NOX emission rate, calculated in accordance with subsection (a) of this section.
(e) An owner or operator of any unit operated with a combination of gaseous (or liquid) and solid fuels shall use a heat input weighted sum of the appropriate emission specifications of §117.105 of this title in calculating the plant-wide emission specification and shall assign to the unit the maximum allowable NOX emission rate, calculated in accordance with subsection (a) of this section.
(f) Units exempted from emission specifications in accordance with §117.103(b) and (c) of this title (relating to Exemptions) are also exempt under this section and must not be included in the plant-wide emission specification, except as follows. The owner or operator of exempted units as defined in §117.103(b) and (c) of this title may opt to include one or more of an entire equipment class of exempted units into the alternative plant-wide emission specifications.
  (1) Low annual capacity factor boilers, process heaters, stationary gas turbines, or stationary internal combustion engines as defined in §117.10 of this title are not to be considered as part of the opt-in class of equipment.
  (2) The ammonia and carbon monoxide emission specifications of §117.105 or §117.110 of this title apply to the opt-in units.
  (3) The individual NOX emission specification that is to be used in calculating the alternative plant-wide emission specifications is the lowest of any applicable permit emission specification determined in accordance with §117.105(a) of this title, the specification of paragraph (4) of this subsection, or when applicable, subsection (i) of this section.
  (4) The equipment classes that may be included in the alternative plant-wide emission specifications and the NOX emission rates that are to be used in calculating the alternative plant-wide emission specifications are listed in the table titled §117.115(f) OPT-IN UNITS.
Attached Graphic
(g) Solely for the purposes of calculating the plant-wide emission specification, the allowable NOX emission rate (in pounds per hour) for each affected unit must be calculated from the lowest of the emission specifications of §117.105 of this title, or when applicable, §117.110 of this title, or any applicable permit emission specification identified in subsection (i) of this section, as follows.
  (1) For each affected boiler and process heater, the rate is determined by the following equation.
Attached Graphic
  (2) For each affected stationary internal combustion engine, the rate is determined by the following equation.
Attached Graphic
  (3) For each affected stationary gas turbine, the rate is determined by the following equations.
Attached Graphic
  (4) Each affected gas-fired boiler and process heater firing gaseous fuel that contains more than 50% hydrogen (H 2) by volume, on an annual basis, may be adjusted with a multiplier of up to 1.25 times the product of its maximum rated capacity and its NOX emission specification of §117.105 of this title.
    (A) Double application of the H2 content multiplier using this paragraph and §117.105(b)(6) of this title is not allowed.
    (B) The multiplier may not be used to increase a limit set by permit.
    (C) The fuel gas composition must be sampled and analyzed every three hours.
    (D) This paragraph is not applicable for establishing compliance with §117.110 of this title.
(h) The owner or operator of any gas-fired boiler or process heater firing gaseous fuel that contains more than 50% H 2 by volume, over an eight-hour period, in which the fuel gas composition is sampled and analyzed every three hours, may use a multiplier of up to 1.25 times the emission limit assigned to the unit in this section for that eight-hour period. The total H2 volume in all gaseous fuel streams will be divided by the total gaseous fuel flow volume to determine the volume percent of H2 in the fuel supply. This subsection is not applicable to:
  (1) units under subsection (g)(4) of this section;
  (2) increase limits set by permit; or
  (3) establish compliance with §117.110 of this title.
(i) When using this section for establishing alternative compliance with §117.110 of this title, the individual NO X emission specification that is to be used in calculating the alternative plant-wide emission specifications is the lowest of the specification of §117.110 of this title, the actual emission rate as of September 1, 1997, and any applicable permit emission specification, in effect on September 10, 1993.

Source Note: The provisions of this §117.115 adopted to be effective June 14, 2007, 32 TexReg 3206